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Grain growth control of isotope exchange between rocks and fluids

¹ Institute of Mineralogy, Petrology, and Economic Geology, Graduate School of Science, Tohoku University, Aoba, Sendai 980-8578, Japan
² Division of Earth and Planetary Sciences, Hokkaido University, Sapporo 060-0810, Japan, and Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Meguro, Tokyo 152-8551, Japan
³ Department of Earth and Environmental Sciences, Rensselaer Polytechnic Institute, Troy, New York 12180, USA

Isotope exchange between fluid and rocks has been traditionally considered to be rate limited by two elementary processes: lattice diffusion in the matrix minerals and dissolution into the fluid followed by precipitation from it. In this study we show the results of high-pressure experiments on ¹⁸O-water infiltration into quartzite that point to a third, highly efficient process: grain growth accompanied by migration of the grain boundaries (GBs) that are isotopically enriched by GB diffusion and surface exchange. We predict on the basis of a mass-transfer mechanism discrimination diagram that this GB sweeping is the primary control on isotopic equilibration under hydrothermal conditions in various fine-grained rocks with low fluid fraction. Grain growth should be considered when interpreting and simulating isotope and chemical composition of rocks and fluids.

Key Words: grain boundary • oxygen isotope • fluid flow • diffusion • quartzite

This article has been cited by other articles:

				H. Yurimoto, A. N. Krot, B.-G. Choi, J. Aleon, T. Kunihiro, and A. J. Brearley Oxygen Isotopes of Chondritic Components Reviews in Mineralogy and Geochemistry, January 1, 2008; 68(1): 141 - 186. [Abstract] [Full Text] [PDF]